The present invention relates to a propellant augmented gas dispensing device, and more particularly to an improved pressure relief assembly for such a device.
Propellant augmented, gas dispensing devices are utilized for a variety of purposes, including the pressurization of inflatable devices, such as escape slides, life rafts, and air bag safety cushions in automobiles. Typical gas dispensing devices of this type have first and second chambers. The first chamber carries a relatively inert gas under pressure, for example carbon dioxide, while the second chamber carries a solid propellant, for example ammonium nitrate. The solid propellant is utilized as an energy source to heat and pressurize the carbon dioxide gas stored in the first chamber to temperatures on the order of 180.degree. F. and pressures on the order of 5000 psi. Normally, the propellant will pressurize the gas in less than one second, at which time an outlet burst disc in the exhaust passage from the propellant chamber will rupture, allowing the pressurized gas to pass through the propellant chamber and out the exhaust passage. The highly pressurized gas is thus available to do useful work, for example inflate a life raft or other suitable device.
These propellant augmented, dispensing devices are designed for operation over ambient temperatures from, for example, -65.degree. to 160.degree. F. If a device is inadvertently exposed to temperatures in excess of the design temperatures, it is possible for the gas pressures within the device to approach the upper limit of the design pressures of the device. It is desirable for the device to have a safety mechanism that relieves the pressure within the device should it exceed a predetermined maximum. It is, however, necessary for such devices to have a burst disc or similar assembly situated between the propellant and the pressurized gas chamber. The rupture disc prevents the pressurized gas from contacting the propellant prior to ignition so that it can be properly ignited. Once the propellant is ignited, the burst disc will release propellant gases into the gas chamber after the pressure in the propellant chamber has reached a predetermined pressure, normally on the order of 500 psi higher than the stored gas pressure. On the other hand, it is desirable to relieve pressure in the gas chamber once it has reached the desired design maximum, for example on the order of 5000 psi. It is furthermore desirable to simplify the pressure relief assembly to reduce overall weight and cost. If possible, it is also desirable to combine the pressure relief assemblies into a single throw-away mechanism. Previous attempts at solving this problem have met with limited success.